Biostratigraphical and palaeobiogeographical patterns of the larger porcelaneous foraminifer Austrotrillina Parr, 1942

Abstract

Among the Tethyan larger porcelaneous foraminifera widespread from the middle–late Eocene to the middle Miocene, Austrotrillina Parr, 1942 is the only genus showing a non-homogeneous shell structure. This consists of a parakeriotheca, coated by a thin, dense tectum. Four Austrotrillina species (A. brunni, A. eocaenica, A. howchini, A. striata) have been often used as biostratigraphical markers in the Mediterranean and Indo-Pacific areas. New materials from southeastern Spain and Central Indo-Pacific (Indonesia, Kita-daito-jima, Kikai Seamount) were studied to assess their taxonomic status, species circumscription and palaeobiogeographical patterns. Based on re-assessed shell structures A. asmariensis Adams is considered a junior synonym of A. brunni Marie.Austrotrillina eocaenica first appears in the middle–late Eocene of Iran. Two Rupelian descendants, A. brunni and A. striata, migrated from the Western Tethys into the Indo-Pacific. Austrotrillina striata reached Indonesia and Western Australia in the Chattian, then disappeared in the Langhian of Kita-daito-jima. Austrotrillina brunni first occurred in the Burdigalian of Indonesia and Western Australia and disappeared in the early Serravallian of Western and South Australia. Austrotrillina brunni and A. striata disappeared in the Serravallian westernmost Mediterranean (southeastern Spain). From the Burdigalian the exclusive occurrence of A. howchini in the Indo-Pacific areas is a possible result of the closing Tethyan Seaway, which differentiated the Mediterranean and Indo-Pacific bioprovinces. This species disappears in the latemost Langhian–early Serravallian of South Australia and in the Kikai Seamount. The palaeobiogeographical distribution of these species suggests an early Miocene active connection of Eastern Africa with the Central Indo–West Pacific.